In biometric authentication relying on a vessel pattern of a living body, images of body sites such as a palm, the back of a hand, and a finger are captured using, for example, near infrared rays. Reduced hemoglobin contained in the vein absorbs near infrared rays, and the vein portion thus appears darker than other portions around this portion. Accordingly, digital image processing extracts a dark portion and extracts a pattern shown by dark lines corresponding to the vessels as a vessel pattern, which is used as information to identify a person. A vessel pattern of a person is registered in advance; when authentication is performed, a vessel pattern of a person to be authenticated is read, and this vessel pattern is verified against the vessel pattern registered in advance to perform authentication.
Meanwhile, a technology is known for non-invasively measuring hemoglobin concentration using the near-infrared spectroscopic imaging method (e.g., non-patent document 1).
A biometric authentication sensor based on a vessel pattern typically has a certain sensing level with respect to the thickness and the size of a vessel image in accordance with a resolution achieved by an image capturing unit and the performance of digital image processing for extracting a dark line from the obtained image. When the vessel at a certain portion indicates a level that is equal to the sensing level of the sensor or lower due to a low temperature, the presence of the vessel at this portion may possibly not be sensed.
A technology is known wherein authentication is performed in accordance with the combination of the fingerprint and the vessel, and, in vessel authentication, characteristics are extracted in consideration of the distribution of and connection between the sizes of vessel patterns.
A technology is known wherein, when the quality of a read image of biometric information is bad, image processing is performed for improving the quality of the read image during authentication processing.
An identification device relying on digital veins is provided with a second light source that emits light to be reflected from a finger and to be incident on an imaging part in order to decrease identification errors such as an error in inserting a finger and an error caused by deformation of a finger. A technology is known for determining whether or not the vessel pattern of an image captured using light from the second light source is clear.
In regard to an in-vehicle fingerprint authentication apparatus, it is known that means is provided for generating a correction value for a fingerprint image signal in accordance with an ambient temperature.
In regard to a biometric authentication device that performs authentication using blood vessel images of a living body, it is known that the temperatures of the living body at the time of registering and the time of collating are detected and that, when a collation error occurs, the cause of the error is estimated from the difference between the temperature at the time of registering and the temperature at the time of collating.
In regard to an authentication apparatus that authenticates a person using a fingerprint, it is known that a temperature and humidity at the time of authenticating are measured and an identification threshold or a forgery threshold to be used for authentication is set in accordance with a temperature or humidity.
In regard to a biometric authentication apparatus that specifies an individual by use of a facial image, a technology is known wherein it is determined which of a plurality of environmental sections the environment for inputting the facial image corresponds to, and, in accordance with the learning frequency of dictionary information at the environmental section at the time of inputting, learning is performed.